vorbis_encode_setup_vbr

declared in "vorbis/vorbisenc.h";

This function performs step-one of a three-step variable bitrate
(quality-based) encode setup. It functions similarly to the one-step
setup performed by vorbis_encode_init_vbr() but
allows an application to make further encode setup tweaks using vorbis_encode_ctl() before finally
calling vorbis_encode_setup_init() to
complete the setup process.

Before this function is called, the vorbis_info struct should be initialized by using vorbis_info_init() from the libvorbis API. After encoding, vorbis_info_clear should be called.